1. Technical Field
The present invention relates to a radiological image detection apparatus for use in a medical X-ray imaging system etc., and a method for manufacturing the same.
2. Related Art
In recent years, a DR (Digital Radiography) using an X-ray image detection apparatus such as an FPD (Flat Panel Detector) for converting X-rays into digital data has been put to practical use. The X-ray image detection apparatus has been being widely used rapidly due to a merit that an image can be confirmed in real time as compared with a background-art CR (Computed Radiography) system using an imaging plate.
Various systems have been proposed for an X-ray image detection apparatus. For example, there is an indirect conversion system in which X-rays are once converted into visible light by a scintillator of CsI:Tl or GOS (Gd2O2S:Tb), and the converted light is converted into electric charges by a semiconductor layer and accumulated.
For example, when such an X-ray image detection apparatus is used in a living body, it is often preferable that the dose of X-rays is low. A scintillator which is high in amount of luminescence and superior in sensitivity is therefore desired. Addition of an activator to a host of a fluorescent material is known as a method for increasing the amount of luminescence of a scintillator (Patent Documents 1 (JP-A-2008-51793), Patent Document 2 (JP-A-2006-064436) and Patent Document 3 (JP-A-2011-017683)). In Patent Document 1, description has been made on a radiological image detection apparatus having a sensor board and a scintillator which includes columnar crystals and on which X-rays are incident from the opposite side to the sensor board, wherein: the density of an activator is increased in an X-ray entrance side region of the scintillator. In the description of Patent Document 1, for example, the activator density on a front end side of each of the columnar crystals is high when the columnar crystals are deposited on the sensor board, and the activator density on a base end side of each of the columnar crystals is high when a substrate on which the columnar crystals are deposited is pasted onto the sensor board.
In Patent Document 2, description has been made on a radiological image conversion panel having a photostimulable phosphor in which a layer with a low intensity of luminescence and a layer with a high intensity of luminescence are laminated alternately in the deposition direction of CsBr:Eu.
Here, the amount of luminescence is increased with increase in the activator density. However, the crystallinity of the scintillator is disordered by activation with high density to thereby cause light absorption and light diffusion. Thus, MTF (Modulation Transfer Function) deteriorates.
In addition, in the description of Patent Document 1, the activator density on the base end side of each columnar crystal or the activator density on the front end side of each columnar crystal is increased in accordance with the configuration about the manufacturing and assembly of the scintillator and the sensor board. However, when the activator density is high on the base end side of the columnar crystal which is a portion of an early stage of crystal growth, MTF is lowered due to deterioration of crystallinity. On the other hand, when the activator density is high on the front end side of the columnar crystal, the strength is lowered due to disorder of crystallinity. Thus, the front end portion of each crystal is easily damaged when the scintillator and the sensor board are pasted or when a load is applied to a scintillator panel. Further, when a protective film is broken or separated from the substrate on the base end side or the front end side where the activator density is high, the scintillator absorbs moisture and the performance thereof deteriorates easily.